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  • Dilute heavily strong acids or alkalines before using them

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pH & Hair

21 September 2005

Hair is made up mainly of proteins and is pretty strong stuff. However, chemical processes can weaken your hair and cause it to break. In this article I’ll explain how the pH of hair products can affect your hair’s condition and how you can avoid unnecessary damage.

The structure of the hair is made of two main parts. The outer layer, called the cuticle consists of overlapping scales which protect the cortex underneath. When your hair becomes damaged the scales of the cuticle can stand out or break off, exposing the cortex and making your hair feel dryer and harder to brush.

The cortex which is in the inner region of the hair is made of a a string of proteins and gives the hair it’s strength and elasticity. This is why damaged hair does not return to shape or even snaps when stretched. The cortex is where menalin (which denotes your natural hair colour) can be found. For this reason most hair colours will need to penetrate to the cortex in order to change your hair colour.

You can measure the pH of anything that is water soluable. The pH indicates how acid or alkaline a substance is. The scale ranges from 0 to 14 with 0 being a very strong acid and 14 being a very strong alkali (aka a base). Both strong acids and alkalis should be avoided as they will burn skin.

Water has a pH of around 7, as does Peroxide and most shampoos. Lemon Juice and Vinegar, both acids, have a pH of around 2 or 3 and baking soda, an alkali, has a pH of around 8 or 9.

Diagram: Cross section of a hair

Hair Colours are Usually Alkaline

Most permanent hair colours are alkaline. When an alkaline substance is applied to hair it opens up the cuticle. With hair colour this allows the mixture to penetrate to the cortex where it can react with the hair’s pigment molecules to produce a colour change. Permanent colours have a pH of around 7-8. With bleach the colour molecules are oxidised, producing the lightening effect. Bleach usually has a pH of around 8 or 9 and if used too often or mixed too strong it will cause the scales in the cuticle layer to break off which causes permanent damage. The layers in the cuticle will no longer lie flat and will stick outward causing hair to snag and tangle. When the scales do not lie flat or when some have broken off the hair is no longer water proof and the cortex is exposed to washing and envirnomental factors. This will cause it to dry out and loose elasticity leaving the hair prone to breakage.

However, you can avoid most of this damage if you only bleach your regrowth each time and do not allow the bleach to overlap onto already bleached hair. Since peroxide has a pH of 7 all the alkalinity comes from the powder. If in doubt mix your bleach to a thinner consistancy with more peroxide and avoid lumps of powder which can cause breakage. If you use a lot of powder the bleach is going to have a high pH which causing damage to the hair.

Acidic Hair Products

Most hair products don’t contain strong acids other than some perming solutions. Conditioner has a slightly acid pH. Mild acid has a an opposite effect to alkalis and flattens the cuticle making your hair easier to comb and look shinier. Many people believe that rinsing hair with vinegar after dyeing helps the longevity of direct dyes such as Manic Panic or Special Effects. This is probably because it closes the cuticle helping the colour stay in the cortex for longer.

Using the pH to your Advantage

So, we know that an alkali will open up the cuticle and an acid will flatten it, so how can we use this to get better hair colour? Let’s assume your hair is already bleached and you’re applying a new shade of colour using something like Directions or Special Effects. If you can get the colour deep into the cortex it will take a longer time to rinse out (these dyes deposit colour molecules into the cortex and fading occurs as the molecules are rinsed out of the cortex). First wash your hair. Hair is coated in a layer of oil to help keep your hair in good condition. This can act as a barrier to direct hair colours like those mentioned above. Now the hair is all clean we can use an alkali to open up the cuticle. A small amount of baking soda disolved in warm water will be adequit. You only need about 1 teaspoon in a pint of water. Keep away from your eyes and allow the mixture to rinse through your hair. Now blow dry the hair until it’s damp. Heat will also help open the cuticle. The hair is now ready to dye. Apply the dye to your hair and leave for 30-40 minutes. Rinse in cold water. Rinse again in a mixture of water and a few tablespoons of vinegar or lemon juice (again, keep away from eyes). Condition your hair leaving the conditioner on for as long as possible and then rinse in cold water. Your hair should now be shiny and will have the best chance of keeping the colour.


  • OMG!!! thank you so much. finally it all makes sense. now i can pass on the info to my club members. i know they're all dying to know. Report Comment
  • You made a typo (or spelling mistake). In the last paragraph, you wrote "adequit". I think you mean "adequate". Good article, though I knew a lot of this already. This is definitely stuff that regular dye users should know! Report Comment
  • This is a must-read for all first time dyers! I share this information with anyone whose head I've dyed in the past couple of years. Report Comment
  • Yeah, this is a great article! I learned everything through trial and error..mainly errors. Been dying my hair for seven years now. But I have my own technique that goes along with this. I wash it with a pH balancing shampoo than let it air dry and use a protein filler or baking soda and water. Than I color. But I use heat directly after, for me this makes it last longer...and for some colors and brands of dye I don't rinse it out-just let it dry in. (doesn't stain as you might think) I don't condition when I color. I have very thick multiracial hair, which tends to be dry so I use olive oil to moisturize it. I have a day out of the week that I wash my hair, and I use the same pH shampoo and an intensive conditoner that I leave on for a while and than I do hot oil treatments. I do color touch ups once a month. All this is just my personal technique that I found to work really well with me and my hair. Everyone's different. Report Comment
  • Does this mean you should use acidic shampoos and conditioners to make your hair smooth and shiny? Report Comment
  • oooo great stuff !! Report Comment
  • Would it be a good idea to use the baking soda mix to open the cuticle before using a treatment on your hair? Report Comment
  • Ive always wondered how the vinegar trick works, thanks :) Report Comment
  • thanks for anouther useful article, now my raw dye should stay in my hair longer than two washes. Report Comment
  • Very interesting stuff. Never heard of the baking soda thing before. A cheap and easy trick! Report Comment
  • great article, gives a good brief idea on how hair behaives. i did my science fair project on hair ph and how bleach effects it. during my background research i ran into this and because of it researched the effect of vinegar on the cuticle scales. Report Comment
  • Good refresher on pH's thanks doll! Report Comment
  • Thank you for the great article! This will be really useful for the hairdressing course I'll be doing! I already have a text book which explains that sort of stuff but I like reading hair science things from loads of different people/sources because it gives me a better understanding overall as the explanations are slightly different each time. Report Comment
  • Thank you, very helpfull. Report Comment

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